1. Field of the Invention
The present invention generally relates to a photo-coupler device, in particular to a photo-coupler device with improved light transmittance and common-mode transient immunity.
2. Description of the Related Art
Photo-coupler is also known as an optical isolator, and abbreviated as PC. The photo-coupler transmits electrical signals by using light as a medium. The photo-coupler has a prefect isolation effect for the input signal and the output signal, and may obtain a wide range of applications in a variety of circuits.
Currently, the photo-coupler has become one of the most popular and the most versatile photoelectric devices. The photo-coupler generally consists of three portions: a light emitting portion, a light receiving portion and signal amplification portion. The light emitting portion may be a LED, which is driven by an input electrical signal to emit a certain wavelength of the light, which is received by a photo detector so as to generate a photocurrent signal, and then the signal is taken as the output after amplification. Thereby an electricity-light-electricity conversion is completed, thus the photo-coupler achieves the function of input, output and isolation.
In addition, since the input and the output of the photo-coupler are isolated from each other, the transmission of the electrical signals has unidirectional characteristics and thus the photo-coupler have a good electrical insulation capability and a noise resisting capability. Further, the input end of the photo-coupler is a current-type low resistance component and having a strong common mode suppression capability. Therefore, in the long-range transmission of signals, the photo-coupler may be employed as an terminal isolation component which may significantly improve the signal-to-noise ratio. Through the use of the photo-coupler, the electrical signals of the source may be prevented from the surge and the unstable condition caused by direct connection of the circuit of a receiving end and the source.
However, in the structure of conventional photo-coupler structure, an indium tin oxide (ITO) layer is disposed on an insulation layer. Since the optical transmittance and the electrical conductive capability of the indium tin oxide layer is unstable, the electrical conductivity of the photo-coupler structure is easily decreased and the reception signal would be inaccurate caused by the interference of the transient noise. Further, the electrical resistance of the conventional indium tin oxide layer is large and during a fast signal transmission of the conventional indium tin oxide layer, the voltage conversion efficiency and the common-mode transient resistance become poor, which leads to the distortion problem of the output signal.